Hey all-

I'm looking for some education on barrel length and rifle twist kn regards to choosing an accurate long range bullet in 5.56/.223.

The rifle is a Colt CAR 6724 24" barrel with 1 in 9" twist.

My understanding is that 1 in 9" obligates me to bullets lighter than 77gr.
Is that correct?
Does the 24" barrel help stability at all or just velocity?
Other than "try a bunch and see what she likes" can anyone recommend a range of projectile weights to stick within?
Any factory loadings that you think will produce good results?
I'm not concerned with terminal performance. Only tiny groups at the longest distances.

Thanks,

Bruce

Helps velocity only.
I've read you can go up to 69gr with 1-9" comfortably (Sierra says 1-10) but haven't reloaded the pile I got for future.
And yes, it will depend on the gun and how it likes the particular bullet

Yep, 1X9 twist 77/75gr bullets become a crapshoot. It gets worse in cold thin air.

Some 1X9" twist will do fine with the 77/75gr. class bullets.

The 69/68gr. bullets will be just fine in that twist rate and 600 yards will be no problem, after that it becomes more sporting!

The B.C. of the 69/68gr. bullets isn't high enough to be really good past 800 yards, not saying that you can't shoot further, but it will be very hard!

The 1X8" twist is the "sweet spot" for .22 caliber centerfire cartages. I don't care if it's a .22-250 or .223 I would like them to be all 1X8" twist, with that one could shoot bullets from 45gr. to 80gr. with no problems and most likely 90gr. VLD bullets. Now that's versatility!

But I digress. With the 1X9" twist, 69gr and lighter is most likely the best bet.


ARman

quote:

Originally posted by KMitch200:
Helps velocity only.
I've read you can go up to 69gr with 1-9" comfortably (Sierra says 1-10) but haven't reloaded the pile I got for future.
And yes, it will depend on the gun and how it likes the particular bullet

Not exactly. Stability is a function of both twist and velocity. Drive a bullet faster and it will be stable from a slower twist.


Berger has a calculator on their website.

quote:

Originally posted by RNshooter:
Other than "try a bunch and see what she likes" can anyone recommend a range of projectile weights to stick within?
Any factory loadings that you think will produce good results?

All of the following should shoot well:
69 SMK -- Federal, Fiocchi, ADI, Black Hills (there should be other options, too)
68 HPBT -- Hornady
69 Scenar -- Lapua, Corbon

69 TMK -- Black Hills, Creedmoor Sports -- IMO the jury is still out on the TMK bullet

There's no guarantee that your rifle will or will not work well with heavier bullets:
73 ELD -- Hornady
75 HPBT -- Hornady
77 SMK -- Federal Fiocchi, Black Hills (there should be other options, too)
77 TMK -- Black Hills, Creedmoor Sports -- IMO the jury is still out on the TMK bullet

quote:

Originally posted by ARman:
It gets worse in cold thin air.

The reason it becomes worse is because cold air is denser, not thinner, than warm air. Air resistance is what causes bullets to become unstable. If it were fired in the vacuum of outer space, a 90 grain 0.224 caliber bullet would be stable if fired from a 1/14" barrel (or slower).

quote:

Originally posted by sigfreund:
If it were fired in the vacuum of outer space, a 90 grain 0.224 caliber bullet would be stable if fired from a 1/14" barrel (or slower).

When Alan Shepard was on the moon, he should have packed an AR-15 along with his golf clubs. Uncertain what kind of trigger control he would have with those gloves, however.

quote:

Originally posted by sigfreund:

quote:

Originally posted by ARman:
It gets worse in cold thin air.

The reason it becomes worse is because cold air is denser, not thinner, than warm air. Air resistance is what causes bullets to become unstable. If it were fired in the vacuum of outer space, a 90 grain 0.224 caliber bullet would be stable if fired from a 1/14" barrel (or slower).

Yeah. That's what I meant. I didn't catch that. Thanks for the fix in information! I can't believe that I missed it!


ARman

quote:

Originally posted by IndianaBoy:

quote:

Originally posted by KMitch200:
Helps velocity only.
I've read you can go up to 69gr with 1-9" comfortably (Sierra says 1-10) but haven't reloaded the pile I got for future.
And yes, it will depend on the gun and how it likes the particular bullet

Not exactly. Stability is a function of both twist and velocity. Drive a bullet faster and it will be stable from a slower twist.

That's true....but unless someone is going to buy the ammo for me, I'm not going to spend the coin on factory match ammo that might work. I'm going to try the loads that I know *should* work.
Buying several different brands of a known good weight to see what a rifle likes is expensive enough without throwing in bullet weights that could be suspect from the start.

Ahem … to review the bidding:

quote:

Originally posted by RNshooter:
Does the 24" barrel help stability at all or just velocity?

quote:

Originally posted by KMitch200:
Helps velocity only [emphasis added]

quote:

Originally posted by IndianaBoy:
Not exactly. Stability is a function of both twist and velocity. Drive a bullet faster and it will be stable from a slower twist.

quote:

Originally posted by KMitch200:
That's true....but unless someone is going to buy the ammo for me, I'm not going to spend the coin on factory match ammo that might work. I'm going to try the loads that I know *should* work.
Buying several different brands of a known good weight to see what a rifle likes is expensive enough without throwing in bullet weights that could be suspect from the start.

Your economic concerns are understandable, but you didn’t mention that at first, and IndianaBoy was responding to your statement above about bullet stability which was the original question pertaining to barrel length. I have always been a little vague about the effect of velocity on stability and appreciate the clarification.

quote:

Originally posted by sigfreund:

quote:

Originally posted by KMitch200:
That's true....but unless someone is going to buy the ammo for me, I'm not going to spend the coin on factory match ammo that might work. I'm going to try the loads that I know *should* work.
Buying several different brands of a known good weight to see what a rifle likes is expensive enough without throwing in bullet weights that could be suspect from the start.

Your economic concerns are understandable, but you didn’t mention that at first, and IndianaBoy was responding to your statement above about bullet stability which was the original question pertaining to barrel length. I have always been a little vague about the effect of velocity on stability and appreciate the clarification.

I agree that match ammo is expensive. Nobody wants to waste ammo or money. But if we want to play the accuracy game to its higher levels, some experimentation with ammo is necessary.

IMO one box of ammo in an AR gives me a pretty good idea if further testing is warranted. In common practice, 4 groups of 5 rounds. A group at 100 yards for benchmark accuracy, then additional groups at progressively longer distances to assess the ammo's ability to maintain vertical. I only test new ammo on days when the winds are reasonable, after I've warmed up, and if I'm shooting well that day.

Early on with my 16" 1/9 twist AR-15 carbine, I found that 75 and 77 grain bullets were on the ragged edge of stability. Hot days and short distances -- the heavy bullets flew well. Cold days and long distances -- accuracy fell off. Only a few boxes of ammo were necessary to make this call. Furthermore, that initial heavy bullet testing indicated that my next carbine barrel needed a little faster twist. I now have a 1/8 twist replacement barrel waiting in the wings, as throat erosion should soon claim that 1/9 twist barrel.

quote:

Originally posted by sigfreund:
I have always been a little vague about the effect of velocity on stability and appreciate the clarification.

Playing with that calculator on Berger's website was interesting.

Velocity of the bullet matters, but not nearly so much as twist rate.

"long range " is the term I get hung up on.

long range for a slice of bread sized target ?
or long range for a back yard shed?

long range to stop a coyote? or long range to stop an elk?

quote:

Originally posted by IndianaBoy:
Velocity of the bullet matters, but not nearly so much as twist rate.

That makes sense in that velocity is seldom mentioned in discussions of bullet stability, and is probably why it’s not something I usually think about.

quote:

Originally posted by bendable:
"long range " is the term I get hung up on.

long range for a slice of bread sized target ?
or long range for a back yard shed?

long range to stop a coyote? or long range to stop an elk?

Me too!
That's why I qualified the question this way:
"I'm not concerned with terminal performance. Only tiny groups at the longest distances."

Bruce

quote:

Originally posted by RNshooter:
I'm not concerned with terminal performance. Only tiny groups at the longest distances.

I assume paper or steel targets, therefore the bullet only has to be flying straight and predictably all the way to the target. IMO this means bullet velocity should be above (roughly) Mach 1.25 at the target. Assuming nothing out of the ordinary with muzzle velocity, assuming 6,000' Density Altitude, distance is limited to roughly 700 yards for the better .223 bullets.

700 yards is doable with a good combined system of gun, ammo, and shooter. Unfortunately, wind really tosses .223 bullets around at such distances.

I have shot SMK 69 grain bullets out to distances where velocity was under Mach 1.0. The bullets held vertical well to about Mach 1.30. With each additional 100 yards in distance, the bullet's ability to hold vertical deteriorated. When I got to 1,000 yards (IIRC Mach .92 to .95), the bullet was tumbling wildly and vertical variation was anywhere from 10 feet above to 10 feet below the point of aim.

quote:

Originally posted by fritz:

I assume paper or steel targets, therefore the bullet only has to be flying straight and predictably all the way to the target. IMO this means bullet velocity should be above (roughly) Mach 1.25 at the target. Assuming nothing out of the ordinary with muzzle velocity, assuming 6,000' Density Altitude, distance is limited to roughly 700 yards for the better .223 bullets.

700 yards is doable with a good combined system of gun, ammo, and shooter. Unfortunately, wind really tosses .223 bullets around at such distances.

I have shot SMK 69 grain bullets out to distances where velocity was under Mach 1.0. The bullets held vertical well to about Mach 1.30. With each additional 100 yards in distance, the bullet's ability to hold vertical deteriorated. When I got to 1,000 yards (IIRC Mach .92 to .95), the bullet was tumbling wildly and vertical variation was anywhere from 10 feet above to 10 feet below the point of aim.

I love picking up bits of information like this.

I picked up a Mega monolithic upper as the start of a Grendel build so I have been looking at external ballistics a bit more seriously than I do for 3-gun where you can pretty much get it all done with 55s as long as you do just a little homework.

quote:

Originally posted by IndianaBoy:
I picked up a Mega monolithic upper as the start of a Grendel build so I have been looking at external ballistics a bit more seriously than I do for 3-gun where you can pretty much get it all done with 55s as long as you do just a little homework.

second #$%&@ try at this, since the site connection @#$%&@ crashed while posting....

I've seen 6.5 Grendel and 22 Nosler do well in team carbine/precision matches. So I compared JBM estimated numbers for Nosler & Grendel to actual figures for my 20" AR-15. Assume 8,000' DA, 2.5" sight over bore, 100 yard zero, target at 700 yards. Drop in MOA, drift in MOA for a 10 mph crosswind.

223 Remy, 69 Federal GMM @ 2811 fps -- 19.0 drop, 7.0 drift

223 Remy, 75 Hornady HPBT @ 2701 fps -- 18.8 drop, 5.9 drift

223 Remy, 75 Hornady ELD-M @ 2727 fps -- 17.7 drop, 5.3 drift

22 Nosler, 77 Nosler HPBT @ 2950 fps -- 14.7 drop, 4.8 drift

6.5 Grendel, 123 Hornady ELD-M @ 2500 fps -- 19.6 drop, 4.5 drift

For now, I'll stick with Hornady 73 ELD. Tempted, but can't justify new upper, optics, and magazines for Nosler or Grendel.

Of course the relative differences are noticeably less for targets under 500 yards.

quote:

Originally posted by fritz:

quote:

Originally posted by IndianaBoy:
I picked up a Mega monolithic upper as the start of a Grendel build so I have been looking at external ballistics a bit more seriously than I do for 3-gun where you can pretty much get it all done with 55s as long as you do just a little homework.

second #$%&@ try at this, since the site connection @#$%&@ crashed while posting....

I've seen 6.5 Grendel and 22 Nosler do well in team carbine/precision matches. So I compared JBM estimated numbers for Nosler & Grendel to actual figures for my 20" AR-15. Assume 8,000' DA, 2.5" sight over bore, 100 yard zero, target at 700 yards. Drop in MOA, drift in MOA for a 10 mph crosswind.

223 Remy, 69 Federal GMM @ 2811 fps -- 19.0 drop, 7.0 drift

223 Remy, 75 Hornady HPBT @ 2701 fps -- 18.8 drop, 5.9 drift

223 Remy, 75 Hornady ELD-M @ 2727 fps -- 17.7 drop, 5.3 drift

22 Nosler, 77 Nosler HPBT @ 2950 fps -- 14.7 drop, 4.8 drift

6.5 Grendel, 123 Hornady ELD-M @ 2500 fps -- 19.6 drop, 4.5 drift

For now, I'll stick with Hornady 73 ELD. Tempted, but can't justify new upper, optics, and magazines for Nosler or Grendel.

Of course the relative differences are noticeably less for targets under 500 yards.

Your post has had me spending time in Excel for the last hour.


Can I ask what barrel length it takes to get 2727 fps for your Hornady 73gr ELD load?


I think a can get a closer to 2550 from a 20 inch Grendel but every barrel is it's own animal. I was charting the Grendel 123gr Lapua Scenar vs the 69gr Lapua Scenar, perhaps I should have been looking at 73/75/77gr 223 ammunition.


It always peeves me a bit that ammunition makers usually list velocity only for a 24 inch barrel, when in reality that is usually not practical.


Even worse is when optics manufacturers use that data to design reticles, instead of real world data from more common barrel lengths.


Of course in some circles 24+ inch barrels are the norm.

quote:

Originally posted by IndianaBoy:
Can I ask what barrel length it takes to get 2727 fps for your Hornady 73gr ELD load?

I think a can get a closer to 2550 from a 20 inch Grendel but every barrel is it's own animal. I was charting the Grendel 123gr Lapua Scenar vs the 69gr Lapua Scenar, perhaps I should have been looking at 73/75/77gr 223 ammunition.

I get 2727 fps from a Krieger 20" barrel for the factory 73 ELD. I get 2653 fps from my 18" Wilson Combat barrel.

I really want Creedmoor Sports' TMK loaded ammo to work in the 20" AR, but accuracy just isn't there. Creedmoor's 77 TMK produces 2815 fps and their 69 TMK produces 2925. I've seen on the webz that some shooters struggle to get the jump right with these TMK bullets.

If 6.5 Grendel had a little more MV, it would be a better long distance round. I wonder if the 123 grain bullet is just a little heavy for the case capacity. Maybe a 6.0 Grendel with the high BC 95-105 grain bullets people use in 6 Dashers would fly better.